1. Field of the Invention
The present invention relates to a plasma treatment method for performing plasma treatment such as sterilization, etc. by applying active species generated by plasma to a target object (target object of treatment) indirectly.
2. Description of the Related Art
In recent years, attempts to perform sterilization of agricultural crops, foods, etc. using active neutral particles in plasma have been made (see the following reference).
Reference: “Agricultural Applications of Plasma: Disinfection to Growth Enhancement”, IEEJ Journal, Vol. 132, No. 10, pp. 702-705, 2012
As apparatuses for generating radicals, in addition an atmospheric pressure barrier electric discharge plasma torch described in the above reference, apparatuses described in International Publications Nos. WO2011/065171 and WO2012/120928 are known.
In the apparatus described in International Publication No. WO2011/065171, an electrode structural body including a first electrode, a second electrode, and a third electrode are provided in a middle of a gas passage. Further, the second electrode is provided on an upstream side of the first electrode, and the third electrode is provided on a downstream side the first electrode. One pole of a pulse power supply is connected to the first electrode, and the other pole of the pulse power supply is connected to the second electrode and the third electrode. Further, the first electrode is provided to cross a first gas passing surface and occupies a part of the first gas passing surface. The second electrode and the third electrode are provided to cross a second gas passing surface and a third gas passing surface and occupy a part of a second gas passing surface and a third gas passing surface, respectively. Accordingly, plasma is generated on the upstream side and the downstream side of the first electrode. Moreover, terminals of the first electrode, the second electrode, and the third electrode do not serve as starting or ending points of electric discharge. Consequently, improvement in the durability of the first electrode, the second electrode, and the third electrode is achieved.
In the apparatus described in International Publication No. WO2012/120928, a passage formation, a transformer, an electrode structural body (anode bar and cathode plate), an anode side feeding path, and a cathode side feeding path are placed in an electrically conductive housing. An extending direction of the anode bar is nonparallel with an extending direction of the cathode plate. The anode bar and the cathode plate cross the passage. The anode bar and the cathode plate are provided apart from each other in an extending direction of the gas passage. The feeding terminal of the anode bar and the positive output terminal of the secondary winding of the pulse power supply are connected electrically, the feeding terminal of the cathode plate and the negative output terminal of the secondary winding are connected electrically. Further, the housing is electrically connected to the cathode side feeding path. In this manner, the waveform of pulse voltage is not disturbed significantly.